There has been a long felt need in the electronic packages container art to utilize an appropriate container or package within which electronic components (e.g., an electronic chip) can be mounted and hermetically sealed.
Historically, electronic chips have been made of ceramic materials such as alumina and, more recently, materials such as gallium arsenide. Thus, some of the requirements for the package or container are that the package be compatible with the electronics (e.g., electronic chips) housed therein. Specifically, the thermal expansion coefficient of the container should approach that of the electronic (e.g., ceramic chip(s)); the package or container should be capable of dissipating any heat generated by the ceramic chip(s); the package or container should be readily fixable (e.g., weldable or solderable) to a lid for hermetically sealing the ceramic chip inside of the package or container; the package should not be adversely affected by any environment to which it is exposed; and the package or container should preferably be relatively inexpensive to manufacture into desirable shapes. Moreover, in many cases it is necessary for electrical leads to be connected with, for example, the ceramic chip(s) or other electronics contained within the package or container. Thus, some means for insulating the electrical leads from the package or container may also be required. Moreover, the electrical leads may need to be hermetically sealed within the container to prevent exposure of the contents of the package or container to any harmful external environment.
Still further, in some cases it may be desirable to provide a coating or series of coatings (e.g., by electroplating, chemical vapor deposition, etc.) onto at least a portion, or substantially all, of a surface of the formed package. Such a coating or layer may: facilitate bonding of electrical leads directly to the electronic package; create a protective layer on the electronic package to enhance the corrosion resistance, erosion resistance, etc., of the package; and/or may function as an electric ground for any electronics (e.g., electronic chip(s), etc.) contained therein. Examples of acceptable coating materials may include Au, Zn, Ni, etc. and mixtures thereof. Thus, a means for coating the surface of the package or container may be required.
The art is replete with attempts to satisfy each of the needs discussed above, however, to date, the art has not satisfactorily solved all of the attendant problems. Description of Commonly Owned U.S. Patent Applications
The subject matter of this application is further related to that of several other copending and co-owned patent applications and co-owned patents. Particularly, these other copending patent applications and co-owned patents describe novel methods for making metal matrix composite materials (hereinafter sometimes referred to as "Commonly Owned Metal Matrix Patent Applications").
A novel method of making a metal matrix composite material is disclosed in Commonly Owned U.S. Pat. No. 4,828,008, issued May 9, 1989, from U.S. patent application Ser. No. 049,171, filed May 13, 1987, in the names of White et al., and entitled "Metal Matrix Composites", now allowed in the United States. According to the method of the White et al. invention, a metal matrix composite is produced by infiltrating a permeable mass of filler material (e.g., a ceramic or a ceramic-coated material) with molten aluminum containing at least about 1 percent by weight magnesium, and preferably at least about 3 percent by weight magnesium. Infiltration occurs spontaneously without the application of external pressure or vacuum. A supply of the molten metal alloy is contacted with the mass of filler material at a temperature of at least about 675.degree. C. in the presence of a gas comprising from about 10 to 100 percent, and preferably at least about 50 percent, nitrogen by volume, and a remainder of the gas, if any, being a nonoxidizing gas, e.g., argon. Under these conditions, the molten aluminum alloy infiltrates the ceramic mass under normal atmospheric pressures to form an aluminum (or aluminum alloy) matrix composite. When the desired amount of filler material has been infiltrated with the molten aluminum alloy, the temperature is lowered to solidify the alloy, thereby forming a solid metal matrix structure that embeds the reinforcing filler material. Usually, and preferably, the supply of molten alloy delivered will be sufficient to permit the infiltration to proceed essentially to the boundaries of the mass of filler material. The amount of filler material in the aluminum matrix composites produced according to the White et al. invention may be exceedingly high. In this respect, filler to alloy volumetric ratios of greater than 1:1 may be achieved.
Under the process conditions in the aforesaid White et al. invention, aluminum nitride can form as a discontinuous phase dispersed throughout the aluminum matrix. The amount of nitride in the aluminum matrix may vary depending on such factors as temperature, alloy composition, gas composition and filler material. Thus, by controlling one or more such factors in the system, it is possible to tailor certain properties of the composite. For some end use applications, however, it may be desirable that the composite contain little or substantially no aluminum nitride.
It has been observed that higher temperatures favor infiltration but render the process more conducive to nitride formation. The White et al. invention allows the choice of a balance between infiltration kinetics and nitride formation.
An example of suitable barrier means for use with metal matrix composite formation is described in Commonly Owned U.S. Pat. No. 4,935,055, issued Jun. 19, 1990 (now abandoned), from U.S. patent application Ser. No. 141,642, filed Jan. 7, 1988 (now abandoned), in the names of Michael K. Aghajanian et al., and entitled "Method of Making Metal Matrix Composite with the use of a Barrier". According to the method of this Aghajanian et al. invention a barrier means (e.g., particulate titanium diboride or a graphite material such as a flexible graphite tape product sold by Union Carbide under the trade name Grafoil.RTM.) is disposed on a defined surface boundary of a filler material and matrix alloy infiltrates up to the boundary defined by the barrier means. The barrier means is used to inhibit, prevent, or terminate infiltration of the molten alloy, thereby providing net, or near net, shapes in the resultant metal matrix composite. Accordingly, the formed metal matrix composite bodies have an outer shape which substantially corresponds to the inner shape of the barrier means.
The method of U.S. Pat. No. 4,828,008 was improved upon by Commonly Owned and Copending U.S. patent application Ser. No. 07/517,541, filed Apr. 24, 1990, which is a continuation of U.S. Patent application Ser. No. 168,284, filed Mar. 15, 1988, in the names of Michael K. Aghajanian and Marc S. Newkirk and entitled "Metal Matrix Composites and Techniques for Making the Same." In accordance with the methods disclosed in this U.S. Patent Application, a matrix metal alloy is present as a first source of metal and as a reservoir of matrix metal alloy which communicates with the first source of molten metal due to, for example, gravity flow. Particularly, under the conditions described in this patent application, the first source of molten matrix alloy begins to infiltrate the mass of filler material under normal atmospheric pressures and thus begins the formation of a metal matrix composite. The first source of molten matrix metal alloy is consumed during its infiltration into the mass of filler material and, if desired, can be replenished, preferably by a continuous means, from the reservoir of molten matrix metal as the spontaneous infiltration continues. When a desired amount of permeable filler has been spontaneously infiltrated by the molten matrix alloy, the temperature is lowered to solidify the alloy, thereby forming a solid metal matrix structure that embeds the reinforcing filler material. It should be understood that the use of a reservoir of metal is simply one embodiment of the invention described in this patent application and it is not necessary to combine the reservoir embodiment with each of the alternate embodiments of the invention disclosed therein, some of which could also be beneficial to use in combination with the present invention.
The reservoir of metal can be present in an amount such that it provides for a sufficient amount of metal to infiltrate the permeable mass of filler material to a predetermined extent. Alternatively, an optional barrier means can contact the permeable mass of filler on at least one side thereof to define a surface boundary.
Moreover, while the supply of molten matrix alloy delivered should be at least sufficient to permit spontaneous infiltration to proceed essentially to the boundaries (e.g., barriers) of the permeable mass of filler material, the amount of alloy present in the reservoir could exceed such sufficient amount so that not only will there be a sufficient amount of alloy for complete infiltration, but excess molten metal alloy could remain and be attached to the metal matrix composite body. Thus, when excess molten alloy is present, the resulting body will be a complex composite body (e.g., a macrocomposite), wherein an infiltrated ceramic body having a metal matrix therein will be directly bonded to excess metal remaining in the reservoir.
Each of the above-discussed Commonly Owned Metal Matrix Patents and Patent Applications describes methods for the production of metal matrix composite bodies and novel metal matrix composite bodies which are produced therefrom. The entire disclosures of all of the foregoing Commonly Owned Metal Matrix Patents and Patent Applications are expressly incorporated herein by reference.